Keyframing from properties panel and from 3d viewport creates different entry on Graph Editor
Rather than the former being a deviation from the latter, the latter seems like an automation implemented for convenience reasons.

Channel groups can be created manually with Ctrl + G. When inserting a Keyframe on a property in the UI rather than with I in the 3D View, in my experience it's usually something miscellaneous like render settings.



The Samples and Preview Samples properties have only one instance per Scene, and the Scene already has an all-encompassing group element in the form of SceneAction.